The GQF Sportsman, the Dickey 1208, and the majority of cabinet style incubators have heating elements on the top of the incubator, as seen in the pictures below. The fan is placed behind the element, and the hot air is bounced off the inside of the door down to the hatching trays. I have previously used an old Lyons electric cabinet that was set up much the same way, but fought cold/hot spots continuously. It always seemed to me that the eggs in the front of the hatching trays always developed faster than those at the rear and bottom, and there were more losses in eggs at the rear or bottom.

So my question is, has anyone built or bought an incubator were the heating element and fan were at the bottom? Since heat rises, it would seem to me that temperatures would be a little more consistent if it were on the bottom, and the fan didn't have to work as hard to circulate air.

Would having the element and water tray at the bottom affect humidity levels?

I need something larger than an LG or Hovabator, but not as large as a Dickey or Sportsman, and I'd like a cabinet style. Unfortunately I dont know of anything that is cabinet style but on a smaller scale, so I'm about to embark on building one around two LG Egg turners. I wondered if having the element on the bottom would help eliminate, or at least reduce the hot/cold spots.

I don't know, but I have been mulling over bulding myself some kind of bator-hatcher-brooder spaceship kind of a thing, and in my mind, the heater would go under the water, which would be in a tub that took up the whole bottom of the cabinet, even if I had to build the cabinet to fit the tub. I would think it would make the water work double duty as a heat sink, to help stabilize temps, and the water being heated evenly would cause the heat to rise more evenly, and the fan would be at the top and force the hot air up top to go back down, from the back of the cabinet toward the front and down... Have not actually made any marks on wood nor bought a new blade for my skilsaw though. still at the thinking stage.

Lets say you took the normal cabinet stile incubator an fliped it forward on to the door. Now cut a new door where the bottom use to be an put the shelves back in it the new way around. Now hot air is circulated down the back,up under the eggs an up threw them to the top. That fixes the cold spots...

There are plans for old stile incubators that had a tank of water in the bottom. Under the tank was a lantern that heated the whole thing an then waters thermal mass made the temp change so slow that it could be regulated.

If you build the standard incubator with air being circulated front to back colder air can sink to the bottom an stay. If you flip the system an make it circulate air top to bottom thermal layering can nolonger happen. I used a side by side fridge for mine becouse it allready had two vertical chambers. I just cut holes between them at the top an bottom an added a fan.

Those plans for that old incubator were from one of the collages websites. A friend had prented them off an showed them to me.

All it really was was a sealed metal can like an old army gas can layed on its side with a vent tube running up. The can was filled with water an a box without a bottom was placed on top of the can. Then the lantern was put under the can an the flame was adjusted to regulate heat. The bigger the water can the slower the temp changes an the more accurate you can be.

I think putting the heating element at the bottom would be problematic. Since the heat rises, if the thermostat were at the bottom, the amount of heat needed to get a stable temp near the bottom would make the top way too hot. Perhaps a top vented bator (constantly vented) and the heating element at the bottom would work out well...the amount of energy that would be used in a set up like that may be prohibitive though...since the heating element would have to be on near constantly. Sorry I'm bouncing around, but I'm just kinda thinking aloud at this point...

I have a homemade incubator at the moment and I have the main heat source on the bottom. At the moment it sems to do great. This incubator was a quick build to just test some of my ideas and now that it has been proven I will be building a much nicer one with auto turners. But like you i thought it would be better to have the heat from the bottom.

I guess if any way worked there would be more incubators of another style. I am thinking about how a chicken sits on their eggs and seems to make sense to me that the heat comes down from above. I wouldn't want to discourage experimentation though as you might be able to find a way to hatch a higher percentage of eggs with a new system. I would want to do a study to see how the heat is circulated in the current systems to see if efficiency could be improved in any new system though.